"I don't know how many years I've got left in me. I keep getting asked the question," Hewitt said an on-court interview. "I'm just pumped to get out on this court and try to put on a great show."

The 4-hour, 3-minute match was the ninth time in the past 10 years that two past US Open title winners faced each other in New York. Hewitt was involved four times, losing the other three.

He won the US Open in 2001 by beating Pete Sampras in the final, and then added a Wimbledon title the following year. But he has been troubled by a series of injuries more recently and lost in the first round at four of his last six Grand Slam tournaments.

"A couple years ago, when I had a couple foot surgeries, I didn't know if I was going to play tennis again," Hewitt said.

"For me to be out here competing, it's a ... lot of fun. I cherish every match I get out there. This is why I still play, to have moments like this," he continued. "Sometimes playing the smaller tournaments, it's hard to get up for. It's not hard to get up for here, that's for sure."

Against the sixth-seeded del Potro, who is 24, the Australian repeatedly scrambled along the baseline to stretch for terrific groundstrokes.

"He's a great champion, a great fighter, and for the second round, he's a very difficult player to play," del Potro said.

While the men hit about the same number of winners -- Hewitt had 42, del Potro 41 -- the biggest difference was in the unforced error department. Looking sluggish at times, and particularly ineffective off his generally weaker backhand side, del Potro finished with a whopping 70 errors, 27 more than Hewitt.

"The wrist is not the way I'd like, but it's not an excuse," said del Potro, who did not try to defend his US Open title in 2010, because of a left wrist injury that required surgery. "Now I have a few days to rest."

It was a match filled with momentum shifts. Hewitt got broken when he served for the first set at 5-4, and again when he served for the fourth at 5-3. Still, he eventually managed to claim the latter by playing what he termed "one of the best tiebreaks of my life."

Sure looked like it. Already ahead 4-0, Hewitt smacked a backhand passing winner down the line from a full stretch, then followed that with a cross-court forehand passing winner to earn set points. After del Potro erased the first with a service winner, he double-faulted to send the match to a fifth set.

And that's when Hewitt really took over, which makes sense considering the two players' records in such lengthy matches. This was the 51st five-setter of Hewitt's career, and he improved to 32-19. Del Potro, meanwhile, dropped to 4-8.

"I hit with him a couple of days ago," Hewitt said. "First time I'd ever seen him."

Novak Djokovic and Andy Murray have met in three of the last four Grand Slam finals, though if they play in the US Open this year, it will be in the semis.

Each took a step forward Friday, shaky at moments and sensational in others, in second-round victories. The top-seeded Djokovic faced two early set points, while defending champion Murray had to go four sets.

Leonardo Mayer, ranked 81st, ran Murray all over the court, but the third-seeded Brit excels at chasing down shots. Murray won the last five games for a 7-5, 6-1, 3-6, 6-1 victory.

Lleyton Hewitt celebrates after ousting Juan Martin del Potro in the second round of the US Open on Friday night. Susan Mullane/USA TODAY Sports

"He's a big hitter of the ball. I had to defend a lot," Murray said in an on-court interview. "I think he played some really, really good tennis. It made for an entertaining match."

After pulling out the first set in a tiebreaker, Djokovic needed less than an hour to close out his victory. The 2011 champion beat 87th-ranked Benjamin Becker of Germany 7-6 (2), 6-2, 6-2.

Becker had a chance to serve for the first set against Djokovic at 5-4. But he wasted the first set point with a forehand into the net and the second when a backhand sailed wide.

"Becker is a quality opponent and he should have won the first set," Djokovic said. "I was fortunate enough to come back and win the first set, and after that, I was much more comfortable on the court."

Djokovic was playing in Arthur Ashe Stadium, where the wind often swirls to players' frustration.

"You need to have this adjustment, footwork, steps, in order to get on the ball," Djokovic said. "I didn't have that in the first set. I was still trying to find my way from baseline, and the other side he was serving well. ... After I played a good tiebreak, everything kind of settled. I started to serve better, started to step into the court, which is important."

Murray was in Louis Armstrong Stadium, a place that had bedeviled him in the past. Last year, he was pushed to four tough sets in the third round and quarterfinals there.

Fifth-seeded Tomas Berdych beat Denis Kudla of the U.S. 7-6 (3), 7-6 (3), 6-3. American Tim Smyczek, ranked 109th, reached the third round at a Grand Slam tournament for the first time. He edged 73rd-ranked Alex Bogomolov Jr. in five sets, needing nearly four hours to win 3-6, 7-6 (6), 2-6, 6-4, 6-4.

During the day session, the only seeded man to bow out was No. 17 Kevin Anderson, a 6-2, 6-2, 6-2 loser against 2006 Australian Open finalist Marcos Baghdatis.

The top-seeded Americans have already won four straight majors -- the so-called "Bryan Slam." If they repeat at Flushing Meadows, they'll join the Australian duo of Ken McGregor and Frank Sedgman as only the second men's team to take all four in a year.

Their win took a total of 55 minutes and after match point, they celebrated with their trademark chest bump.